1. Field of the Invention
This invention relates to an improved method and apparatus for detecting the singlet oxygen emission produced during photoradiation when a chopped source of optical radiation is used to excite a photodynamic sensitizer.
2. Description of Prior or Contemporary Art
When certain non-toxic photodynamic sensitizers, such as hematoporphyrin derivative (HPD) and components thereof, are injected intravenously into the human body, they are selectively retained by cancerous tissue. Thus, two or three days after injection, significantly higher levels of the photodynamic sensitizer are retained in malignant tissue. The tumor is then exposed to a therapeutic light and this light energy causes the photodynamic sensitizer to be excited to an energetic metastable triplet state. Through a direct intermolecular process, the sensitizer transfers this energy to oxygen molecules present in the tissue and raises them from the ground triplet to the first excited electronic singlet state, .sup.1 0.sub.2 [symbolic designation of molecular oxygen in the .sup.1 .DELTA.g electronic state]. The singlet oxygen, .sup.1 0.sub.2, attacks and functionally destroys vital cellular components ultimately inducing necrosis and destroying the cancerous tissue. The advances and problems associated with this cancer treatment are addressed in an article by Thomas J. Dougherty et al entitled "Photoradiation Therapy for the Treatment of Malignant Tumors" published in Cancer Research, Vol. 38, pages 2628-2635 (1978).